The field of high-temperature superconductivity can trace its origins to the discovery by Bednorz and Muller, Z, Phys. B64, 189 (1986) less than two years ago. Since that time, the search for new high-T.sub.c ceramic oxide superconductors has been mostly Edisonian in nature. That is, mix this with that, heat under oxygen to 800.degree.-1100.degree. C., cool slowly, and test for superconductivity. This approach appears to be the method of choice until sufficient knowledge is gained to establish the scientific principles necessary to design and synthesize new single-phase, high-T.sub.c superconductors capable of handling high current densities.
Within the last year, a number of fundamental requirements have been established with regard to the ceramic molecular structure necessary to obtain high-T.sub.c superconductivity. For those oxides exhibiting T.sub.c &gt;90K, these requirements include: a layered perovskite, K.sub.2 NiF.sub.4, orthorhombic oxide structure; a single-phase material of approximate composition, LBa.sub.2 Cu.sub.3 O.sub..about.6.5, where L is a lanthanide metal; or Bi.sub.2 Sr.sub.3-z Ca.sub.z Cu.sub.2 O.sub..about.8, where z ranges from 0.4-0.9, CuO.sub.2 layers with polymeric Cu--O bonds. The ceramic structure is often prepared in an oxygen-rich atmosphere to avoid oxygen vacancies. Additionally, it now appears that molecular requirements for all high-temperature superconducting ceramics includes a lanthanide or equivalent-sized trivalent ion, an alkaline earth, copper, and oxygen (Sheng et al., Nature, 332, 55 (1988)).
More recently, Guo et al., Science, 239, 896 (1988), have reported that superconducting ceramics having structures represented by empirical formulae La.sub.2-x Sr.sub.x CuO.sub.4 and YBa.sub.2 Cu.sub.3 O.sub.7-x have (Cu--O).sub.n sheets or chains in which the adjacent (d.sup.9) Cu(II) sites are antiferromagnetically coupled. Subramanian et al., Science, 239, 1015 (1988) also report the existence of CuO.sub.2 layers with Cu--O bonds in the newly discovered Bi.sub.2 Sr.sub.3-z Ca.sub.z Cu.sub.2 O.sub..about.8 120K superconducting material. Whether the new Tl.sub.2 Ba.sub.2 Cu.sub.3 O.sub..about.8 superconducting material reported by Sheng et al. also contains polymeric Cu--O bonds remains to be seen.
Still other properties of high-temperature, superconducting ceramics must be realized before these materials can become truly useful. For example, to use the new superconductors in many applications, these materials must be able to carry large current densities at high fields. A number of authors have stated that porosity has limited their ability to achieve high current densities or to accurately establish the density of states from the slope of H.sub.c2 at T.sub.c. The low current densities presently found in these ceramics may also be due to a combination of phenomena, including single-crystal anisotropy, regional superconductivity degradation at grain boundaries, and pinning variation, all recently received by Geballe et al., Science, 239, 367 (1988).
Finally, an important physical property that is a prerequisite to these new superconducting materials being transformed from materials of academic interest into materials of practical application is the capacity to be fabricated into fibers for use in superconducting magnets or thin films for microelectronic applications. Current ceramic processing methodology relies on high-temperature, energy- and equipment-intensive techniques to form fully dense ceramic shapes. A typical example of a current fabrication technique employs the sol-gel approach coincident with heating and annealing under pressurized O.sub.2 (see, for example, Iqbal et al. Nature, 331, 326 (1988)). Sol-gel methodology requires a hydrolysis or alcoholysis step to form a spinnable material. The hydrolysis or alcoholysis step often leads to gels whose viscosity is difficult to control and, thus, unsuitable for use in most fabrication techniques.
Accordingly, a need exists for a process of producing a ceramic precursor that is capable of being fabricated into useful shapes such as fibers and films, that, can be transformed into a high-temperature superconducting ceramic of the desired shape.